The invention relates to a double-mass flywheel to be positioned in the drive train of a motor vehicle powered by an internal-combustion engine.
From DE-A-37 21 712, a double-mass flywheel is known that has two flywheels pivoted relative to each other and coupled to each other with torsional flexibility by a torsional vibration damper. While one of the two flywheels is fixed to the crankshaft of the internal-combustion engine, the second flywheel bears a friction clutch by means of which the gears further down the drive train can be disconnected when the internal-combustion engine is started or a gear change is effected.
In the known double-mass flywheel, the first flywheel contains a channel encircling the axis of rotation, in which several comparatively long helical springs are positioned, each individually controlled through endshoes of the torsional vibration damper. The helical springs are connected parallel to each other but, because of their length, they permit a comparatively large relative angle of rotation between the two flywheels. The channel is at least partially filled with a viscous lubricant in order to reduce friction.
In operation, as a result of compression and centrifugal force and because of their length, the helical springs of the known double-mass flywheel are pressed against that inner wall of the first flywheel which bounds the channel radially outwards. Due to the friction between the helical springs and the inner wall surface, a high basic friction arises between the flywheels, even at low rotational speeds and small angles of twist.
Furthermore, in a double-mass flywheel of the type described above, the use of wedge pieces to bend the long helical springs that are positioned in the channel and, at the points of bending, to give them sliding support against that inner wall of the first flywheel which bounds the channel radially outwards, is known from the German utility model 90 17 936.
In the not prepublished but higher-priority German patent application, DE 41 28 868 (corresponding to the U.S. patent application Ser. No. 07/931 932) it is proposed that the two flywheels be coupled with each other with torsional flexibility, by means of at least one set of helical-spring elements that are separate but connected in series. The circumferentially outermost helical-spring elements are guided in spring pots or endshoes, while the ends of adjacent helical-spring elements that are turned towards each other are guided in sliding shoes. Both the sliding shoes and the endshoes are in turn guided in a channel of one of the flywheels that encircles the axis of rotation of the flywheels.
It has turned out that the endshoes in particular are subjected to high mechanical loading, particularly when an attempt is made to keep the basic friction of the torsional vibration damper low by suitably dimensioning the endshoes.